Automatic control of variable physical characteristics



Oct. 11, 1938. A. CALLENDER 2,133,246

TERISTTCS AUTOMATIC CONTROL OF VARIABLE PHYSICAL CHARAG ZSheets-Sheet 1 hvenW ALBLQT @LLENDE/Q Filed June 14, 1955 Oct. 11, 1938. A. CALLENDER 2,133,246

AUTOMATIC CONTROL OF VARIABLE PHYSICAL CHARACTERISTICS -Filed June 14, 1935 2 Sheets-Sheet 2 3 E K r; U

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l I M2 Patented Oct. 11, 1938 v I UNITED STATES PATENT OFFICE AUTOMATIC CONTROL OF VARIABLE PHYSICAL CHARACTERISTICS Albert Callender, Winnington, Northwich, England, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain Application June 14, 1935, Serial No. 26,696 In Great Britain June 20, 1934 10 Claims. (Cl. 236-74) This invention relates to the automatic control sponding change in the compensating effect, the of variable physical characteristics, for example volume, as measured up to a predetermined level, temperature or pressure, and in general of any that is immediately available for a body of the physical characteristic a change in which can same liquid in communication with the liquid be translated into a displacement of matter by constituting the aforesaid surface), it causes this 5 means of a suitable indicating or recording inlevel to follow closely in stepwise manner, Withstrument. in predetermined limits, the movements 'of the Various systems of automatic control of variindicating member, and further, the arrangeable physical characteristics are known at the ment being such thatthe aforesaid liquid level present time, some of which aim at a system in tends to return to a predetermined level corre- 10 which any change of the characteristic is folsponding to the desired value of the characterlowed by a compensating action the rate of which istic to be controlled, by means of liquid flow is a function of the rate of. change of the charthrough a resistant path preferably between the acteristic and also of the absolute magnitude of body of liquid the surface of which follows the the deviation of the same from the desired value, movements of the indicating member and an ex- 15 and in which the characteristic will arrive at the ternal body of liquid of such a magnitude that desired value without hunting. These known the level of the same will be substantially un- I systems are complicated in construction and affected by said flow and the level of which is therefore costly and not easily repaired in the set to the desired value of the characteristic.

event of their failing in service. Those systems By the term coupling means is to be under- 20 which depend for their compensating action stood any form of connection between the comupon a series of impulses at uniform short time pensating means and the level of the liquid surintervals have the disadvantage that considerface, such that any change in the position or able wear and tear of the operating parts takes setting of the compensating means is caused to 5 place. influence the level of the liquid surface by chang- The principal object of the present invention ing, by an amount dependent upon and preferis to provide a system for the automatic control ably sensibly proportional to the corresponding of a variable physical characteristic which satischange in the compensating effect, the capacity fies all practical requirements as to efficiency, of the liquid container as measured up to a fixed even should there be an interval of time between arbitrary datum level. The capacity of the liquid 30 the occurrence of any compensating action and container is the space therein bounded by solid the effect of such action upon the characteristic Walls, by the said datum level and by the outlet being controlled, and which is nevertheless sim- 0 e resistant D A ple in construction and economical in operation. It is possible to arrange for t predetermined A further object of the invention is to provide an liquid level to be disp accordance With 35 automatic control system which is self-adjusting any desired behaviour of the characteristic. For in the sense that no external adjustment is reexample, the system ay be applied to the autoquired to enable it to maintain the desired value matic control of a temperature which is required of the characteristic in spite of permanent or to change with time.

40 prolonged changes in any conditions liable to In a modification of the system the afor ai 40 affect the same. volume, as measuredv up to the predetermined The essential feature of the improved system level, is further changed by an amount dependis that the relative movements of (1) an indient upon the mag itu o a further Character eating member tracing the variations of the istic, hereinafter referred to as a causal char- 5 characteristic to be controlled and of (2) the acteristic, t Variations of Which y be level of a liquid surface are utilized, through a pected to lead to variations of the characteristic relay system, to operate compensating means to be controlled. tending to restore the desired value of the char- Further features of the invention relate to aoteristic, the resulting action of the compenv means for compensating for backlash or lost mosating means being such that, (through a coution which may exist between the position or set- 50 pling means by which any change in the position ting of the compensating means itself. and whator setting of the compensating means is caused ever external part of, or drive to, the comto influence the level of the liquid surface by pensating means is utilized for coupling to the changing, by an amount dependent upon and automatic control system, and to means for preferably sensibly proportional to the corre obtaining a suitable-compensating effect in cases 55 where the compensating effect due to a given displacement of the compensating means is not proportional to that displacement.

In a preferred form of the invention the indicating member carries two pairs of vertical wires, the lower ends of which terminate in points at slightly different heights. and are adapted to make electrical contact with a mercury surface. Each pair of points is wired to a system of relays in such a way that when the upper point touches the mercury surface a circuit is closed and remains so until the lower point leaves the mercury surface, and when the lower point leaves the mercury surface the circuit is broken and remains so until the upper point touches the mercury surface. The two pairs of points are arranged at slightly different heights; when the circuit controlled by the upper pair is in the closed condition, the compensatingmeans-due to electrical or other actuating mechanism, for example, oil pressureis operating in that direction which ultimately tends to raise the points, and when the circuit controlled by the lower pair is in the open condition the compensating means is operating in that direction which ultimately tends to lower the points; when the circuit controlled by the upper pair is in the open condition and when simul taneously the circuit controlledby the lower pair is in the closed condition, the compensating means is stationary.

An advantage of this system is that chattering of the relays due to incidental makes and breaks of contact at the mercury surface because of vibration or other causes, is eliminated.

The invention will be better understood by reference to the accompanying drawings, in which:-

Figure 1 is a diagrammatic arrangement of an automatic control for the temperature of a sys tem to which heat is supplied by means of a heating medium, e. g. steam, the flow of which can be controlled by a valve.

Figure 2 is a diagrammatic arrangement showing in principle an electrical relay circuit suitable for use in connection with the arrangement of either Figure l or Figure 3.

Figure 3 is a diagrammatic arrangement of the system of Figure 1 modified by an additional change of the aforesaid available volume dependent upon fluctuation of the pressure of the heating medium.

It will be understood that the systems shown in the drawings may be applied to the control of any variable physical characteristic, although for the sake of simplicity reference is made to temperature. The systems shown in the drawings are intended to be examples illustrative of the principles of the invention, and the invention is not limited to these examples.

Referring to Figure l, the supply of heating medium, e. g. steam, to the system the temperature of which is to be controlled, is via a pipe I having a regulating valve 2, this valve being op erated by a motor and reduction gearing which are not shown in the drawings. The indicator of the valve carries a pulley 3 to which is attached a chain 4 passing over a pulley 5 and having a counterweight 6 at its free extremity.

A second pulley 1, which is co-axial with the pulley 5, is connected to the latter by means of an adjustable pin and slot device so as to permit of a small predetermined amount of free relative movement of the two pulleys, indicated by the angle A. This free movement corresponds to the backlash (if any) between the point of attachment of the valve indicator and the valve itself. The second pulley I carries a chain 8, one end of which is free and carries a counter-weight 9 while the other end is attached to a cam wheel [0, to which is fixed a drum H carrying a chain l2. The free extremity of the latter is connected to an extension I3 fitted to a tubular vessel I4 containing a body of mercury IS. The cam wheel I is so shaped that the movement of the vessel I4 is substantially proportional to the change in the rate of flow (quantity per unit time) of the heating medium past the valve 2, which results from alteration of the valve setting.

The arrangement is such that when the pulley 3 moves as the valve is opened, the vessel 14 is lowered, and when it moves as the valve closes the vessel I4 is raised. The power operating the valve is controlled by relays operated in accordance with the relative positions of the indicating member I! and the surface 30 of the mercury in the vessel 14, the arrangement of the relays being explained below with reference to Figure 2. A light brake l6 acting on the spindle of the drum I l ensures that the backlash between the pulleys and 1 is normally fully taken up one way or the other.

As will be seen later, the relay system causes valve 2 to move in such a way that the mercury surface 30 in vessel I4 follows closely in stepwise manner the movements of the indicating member l1. Mercury in a reservoir I8 is connected via capillary tube H! to the mercury in vessel [4. Mercury flows through the capillary tube l9 whenever the surface level of the mercury in IQ is difierent from that in the reservoir H3, at a rate proportional to the existing difference in level at any moment. The reservoir 18 has such an area that the mercury level within it remains sensibly constant, and therefore the surface 30 will always tend to the same level, notwithstanding permanent or prolonged changes in the position of the vessel M as a result of permanent or prolonged changes in some condition or conditions tending to affect the value of the characteristic to be controlled. Thus the valve is free to settle anywhere within its working range and no external adjustment of the system is required to enable it to maintain the desired value of the characteristic in spite of permanent or prolonged changes in any condition liable to affect the same.

If desired, the reservoir l8 may be moved so as to displace the standard mercury level in accordance with any desired behaviour of the characteristic. Thus if the temperature is required to increase progressively with time, the reservoir l8 will be raised in the appropriate manner.

Referring now to Figure 2, the indicating member (ll in Figure l) which rises as the tempera ture rises, carries four wires the lower ends of which terminate in points I'Ia, l1b,-l|c and 1 Id at slightly different heights. The points 11a and I'll) are wired to a relay system comprising a solenoid S1 and a switch 2| operated thereby, the points I and lid are wired to a similar relay system comprising a solenoid S2 and a switch 22 operated thereby. The solenoids S1 and S2 are connected to the main terminal M1 and the other main terminal M2 is connected to the mercury I 5 via contact 20. It will be understood that where necessary, e. g. to limit sparking at the contacts, amplification of the current flowing as a result of contact between points carried by the indicating member and the mercury, may be employed, although f r the sake of simplicity demotor operating the valve- 2 of Figure 1, 'via main terminal M3, resistance'R, contacts 9, h,

motor armature and back via contacts 2, 7' to main terminal M4. This causes the valve to open and the vessel M to descend by a corresponding amount. The resistance B. may be regarded as a permanently inserted starting resistance for the motor and is conveniently inserted in this position to prevent short-circuiting across the mains the switches 2| and 22. K 7

Solenoid'S1 remains energized as "long as th point 11b is submerged, notwithstanding any breaking of contact between I la and the mercury surface, but as soon as point I'll) leaves the mercury surface the solenoid S1 is de-energized and the switch 2! falls, breaking the circuit to the motor.

If the point l'ld, which is slightly lower than l'lb, leaves the mercury surface, solenoid S2 is de-energized and switch 22 drops to open contacts 7c, Z; and close contacts 111., n; and o, p. The switch 22 remains in this position until the point l'lc meets the mercury surface, when the solenoid S2 is again energized. It will be seen that when M3, M4 due to possible accidental movements of the switch 22 closes the contacts m, n; o, 11, current can flow to the armature C via contacts m, n and back via contacts 0, p, and that the circuit is such that the current is supplied to the motor in the direction opposite to that following the closing of switch 2|. Thus the valve is caused to close and the vessel l4 ascends by a corresponding amount. The stepwise movement of the mercury surface 30 takes place downwards between the points Ila and Nb, or upwards between the points I and I'Id respectively according as the group of points as a whole is tending to enter or leave the mercury.

Main terminals M5 and M6 denote the terminals of the field winding of the motor. It is not necessary that the Voltage across terminals M1, M2 should be the same as that across M3, M4 OI M5, M6.

Figure 3 shows how the effect of variations in a causal characteristic may be taken into account without waiting for the system to reflect such variations through variations of the characteristic to be controlled. The pulley 3 carried by the valve indicator has attached to it a chain 4, passing over a pulley 5 and connected to a cam wheel ll] as in Figure 1. (For the sake of simplicity the backlash compensating arrangement of Figure 1 has been omitted in Figure 3.) A chain l2 attached to the drum H of the cam wheel passes over a pulley 25 and is attached to the extension I3 fitted to the mercury vessel M.

The pulley 25 is supported by a chain 24 passing over pulleys 26 and 21 and attached to a piston 28 which moves in accordance with the pressure of the heating medium in the pipe I. If the pressure rises, which would lead eventually, i. e. after an interval of time peculiar to the system under control, to an increase of temper ature, the vessel I4 tends to fall by a corresponding amount, causing the control system to operate as though the temperature had already risen, although it has not yet been affected by the increase in pressure of the heating medium. Thus the control system anticipates'the effect of variations in the causal characteristic and a smoother control is obtained than would be the case if the basic system of Figure l were employed.

As many varied and apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is-to be understood that I do not limit myself to the specific embodiments thereof, except as defined in the appended claims.

I claim:

1. A system for the automatic control of a variable physical characteristic, comprising an indicating member tracing the variations of the characteristic to be controlled, compensating means operable to maintain the desired value of the characteristic, electrical means, including contact means operated by said indicating member and movable contact means associated therewith, for controlling the operation of said compensating means, coupling means associated with said compensating means and said movable contact means whereby said movable contact means is caused to follow closely in stepwise manner, within predetermined limits, the movements of the indicating member, and slowly acting re-- storing means, operating independently of said.

compensating means, and arranged to restore said movable contact means to the particular predetermined position which corresponds to the desired value of the characteristic under control.

2. A system for the automatic control of a variable physical characteristic, comprising an indicating member tracing the variations of the characteristic to be controlled, compensating means operable to maintain the desired value of the characteristic, electrical means including contact means operated by said indicating member and liquid contact means associated there- With for controlling the operation of said compensating means, coupling means associated with said compensating means and said liquid contact means whereby the level of the surface of said liquid contact means is caused to follow closely in stepwise manner, within predetermined limits, the movements of the indicating member, and means for gradually returning the level of the surface of said liquid contact means to a predetermined level corresponding to the desired value of the characteristic to be controlled, independently of said compensating means.

3. A system for the automatic control of a variable physical characteristic, comprising an indicating member tracing the variations of the characteristic to be controlled, a bodyof liquid, compensating means operable to maintain the desired value of the characteristic, means including a relay system for operating said compensating means, coupling means associated with said compensating means and said body of liquid, relative movements of said indicating member and a surface level of said. body of liquid acting through said operating means to control the operation of said compensating means, said compensating means being associated with said cou pling means whereby the surface level of said bodyof liquid is caused to follow closely in stepwise manner, within predetermined limits, the movements of the indicating member, and means including a resistant path for flow of liquid for gradually returning the aforesaid liquid surface level to a predetermined level corresponding to the desired value of the characteristic to boomtrolled.

4. A system as claimed in claim 3, in which the liquid level tends to return to the predetermined level .as a result of liquid flow through a resistant path between the body of liquid the surface of which follows the movements of the indicating member and an external body of liquid of such a magnitude that the level of the surface of the same is substantially unaffected by said flow and the level of which is set to the desired value of the characteristic.

5. A system as claimed in claim 3, in which the predetermined level is displaced in accordance with any desired behavior of the characteristic.

6. A system as claimed in claim 3, in which the liquid level which follows the movements of the indicating member is subjected also to a displacement dependent upon the magnitude of a causal characteristic.

'7. A system as claimed in claim 3, in which the relative movements of the indicating member and of the liquid level are those of a four-point electrical contact and a conducting liquid surface.

8. A system as claimed inclaim 3, in which means for compensating for backlash or lost motion are provided in the connection between the coupling means and the compensating means.

9. A system as claimed in claim 3, in which means for compensating for backlash or lost motionare provided in the connection between the coupling means and the compensating means, said backlash compensating means comprising two coaxial pulleys having an amount of free relative movement corresponding to the backlash.

10. A system as claimed in claim 3, in which the coupling means between the compensating means and the liquid level is adapted to modify the effect of displacement of the'compensating means in cases where the compensating effect due to a given displacement of the compensating means is not proportional to that displacement.

ALBERT CALLEN'DER. 

